The article didn't report about anyone else running so it wants us to believe just those three ran it so I am wondering if anyone on Dave's ran it so I can prove the article wrong and brag to my students how clever I was in figuring this out.

I knew a lot of people who ran it and I was there for some of the finish, its the third biggest marathon in Korea after Seoul International and Chuncheon (which was last week), gets around 15-20,000 runners

It's not as bad as it used to be (Seoul has been working quite hard to reduce pollutants), and if you time your runs properly (e.g. evening, NOT during rush hour, or days when you can taste/see it in the air), it's not really noticeable. I have mild asthma, run 4 days a week, and have yet to be too troubled by it.